Something that's over looked during CCNA/CCNP studies is the actual switching that's done on the router. Of course the switching a router does and the switching done on an actual switch is completely different. When speaking of switching on a router it deals with the process of forwarding a packet from one interface on the router to another interface on the same router. This process can be extremely CPU intensive for the router to do. However with the use of certain router switching tecnologies such as "Fast Switching" and Cisco Express Forwarding (CEF) you can significanlty decrease the amount of work the router's CPU has to do.
In the lab I created, I told the internal router to ping the "website" router with 1000000 packets (to simulate traffic). While doing this I disabled CEF and Fast Switching note what happened below:
Note that each exclamation point means that the packet was successfully forwarded and that each period means that the packet was dropped. Looking near the end of the picture you can see when I disabled CEF and the packets were too processor intensive for the router to handle and queue so it started dropping packets to keep up with demand. For testing purposes I increased the packet size to help bog down the router so that you can see the example shown.
